1. Field of the Invention
The present invention relates to an endoscope image processing apparatus for reducing or eliminating a smearing component in an imaging signal produced in an imaging means which is caused by a high luminance light beam such as a laser beam for a treatment.
2. Description of the Related Art
Recently, endoscopes have been widely used to observe organs in a body cavity by inserting a slender inserting portion into the body cavity and to carry out various medical treatments by using a treatment device inserted through a treatment device channel when necessary.
Sometimes, a medical treatment is carried out by inserting a laser beam guide probe for executing a laser treatment as one of treatment devices though the treatment device channel.
Further, various video scope systems using a solid imaging device as imaging means such as a charge coupled device (CCD) have been proposed.
Japanese Patent Unexamined Publication No. 60-85727 (1985) discloses a countermeasure for image deterioration caused by halation in an imaging apparatus for imaging an image of an endoscope. This publication discloses a trans-endoscope imaging apparatus for reducing a charge accumulation time of picture element cells to halation by controlling the charge accumulation time of a solid imaging device to the picture element cells for each block thereof.
Japanese Patent Unexamined Publication No. 1-200783 (1989) discloses a circuit having the following circuit arrangement as a bright point reduction circuit. The reduction circuit detects a bright point component of a video signal having passed through a BPF (band pass filter) or an HPF (low pass filter) by a bright point detection circuit as well as restricting the bright point component of the video signal passing though a bright point suppression circuit by use of the detected bright point component.
When a treatment is to be carried out by a laser probe under a trans-endoscope, halation is caused in an observation screen by a laser beam. Because the laser beam is irradiated while a solid imaging device transfers image data, smearing is caused in the screen by the laser beam and adversely affects the observation screen.
The aforesaid solid imaging device includes a charge transfer type imaging device represented by a CCD (charge coupled device) and a significant amount of smearing is produced in this transfer type device.
The CCD as the charge transfer type device generally includes an FT (frame transfer) system and an ILT (interline transfer) system which are mounted not only on endoscopes but also on video cameras. A CCD employing the FT system shown in FIG. 4(a) includes photosensitive units 51 having a plurality of picture element cells for subjecting an incident light beam to photo-electric conversion, shaded accumulation units 52 for transferring charge accumulated by the photosensitive unit 51, and a shaded output unit 53 composed of a reading register.
A CCD employing the ILT system shown in FIG. 4 (b) includes photosensitive units 54 having a plurality of picture element cells for subjecting an incident light beam to photo-electric conversion and accumulation units 55 for successively transferring charge accumulated by the photosensitive units 55, the photosensitive units 54 and the accumulation units 55 being alternately disposed, and an output unit 56 for outputting signal charge read with respect to each line from the accumulation units 55.
Although the FT system CCD has a chip the size of which is made relatively large and cannot intrinsically prevent photographic fog caused at the photosensitive units even if a transfer speed is increased. Thus, although interference is liable to occur, the FT system CCD has a good light utilizing efficiency. On the other hand, the ILT system CCD is contrary to the FT system CCD.
As shown in FIG. 2, an output image shown in FIG. 1 is an image when a CCD 50 images a subject to which a laser beam spot is irradiated and smearing occurs therein.
FIG. 3(a)-FIG. 3(d) schematically show a state in which smearing occurs and FIG. 3(a) and FIG. 3(c) are cross sections in the transfer direction of the CCD. Further, FIG. 3(b) and FIG. 3(d) show the states of image data.
First, a laser beam (actually, reflected right thereof) is incident on the CCD 50 during an exposure period as shown in the upper portion of FIG. 3(a). Next, as shown in the middle portion of FIG. 3(a), transfer of charge is started and the charge accumulated in the photosensitive units during an exposure period is successively transferred. Signal charge, which was produced by a light beam continuously incident on the photosensitive units during the reading period of the CCD, is added to previously transferred charge and a false signal is detected and thus smearing occurs. FIG. 3(b) schematically shows the state of image data after the completion of the transfer. More specifically, smearing occurs in an image at the upper portion of the position where a laser beam was irradiated (the position where transferred charge which passed through the laser irradiated position was previously accumulated).
The lower portion of FIG. 3(a) shows the state of the CCD just before the second transfer and the transfers to be executed thereafter, wherein charge caused by being exposed by a laser beam in the first transfer process remains at the lower portion in a transfer direction (on a route through which charge at a laser irradiated position passes). Then, the second transfer is completed through the respective steps of in process of exposure, transfer start and transfer end shown in the upper view, middle portion, and lower view of FIG. 3(c). Therefore, image data obtained after the completion of transfer includes a false signal resulting from the remaining charge in the first transfer in addition to the charge accumulated by the continuously incident laser beam, as shown in FIG. 3(d). As a result, smearing occurs linearly in the transfer direction, i.e., in a vertical scan line direction, as shown in FIG. 1. The smearing occurs in a white band shape having a width corresponding to a spot diameter of a laser beam, and makes an observation screen very difficult to observe and adversely affects the diagnosis of an image.